The present invention relates to a power detecting element for detecting the power of a wide-band RF signal and a power detecting device using the same and, more particularly, to a wide-band RF signal power detecting element which has an improved frequency characteristic and can be easily manufactured, and a power detecting device using the same.
As is well known, to detect the power of a RF signal over a wide band, it is possible to use a diode detecting system which detects a signal by using a diode and a thermocouple system which allows a resistor to absorb a signal and detects heat generated by the resistor by using a thermocouple.
The diode detecting system has the advantage that a response is obtained with almost no delay when an input signal is supplied to the diode.
This diode detecting system, however, has the problem that the detection accuracy is low because the system is readily influenced by the signal waveform and the signal level.
Additionally, the junction capacitance of the diode makes it difficult for the diode detecting system to detect the power of a RF signal of millimeter waves or more.
On the other hand, the thermocouple system cannot achieve such high-speed responses as in the diode detecting system, because heat is generated by supplying a signal to the resistor.
This thermocouple system, however, has the advantage that the system can accurately detect the power of a signal without being influenced by the signal waveform.
The present applicant has disclosed a power detector (element) and a power detecting device using this thermocouple system in International Publication No. WO88/03319 (Japanese Patent Application No. 62-506672).
As shown in FIG. 20, this power detector includes a first thermocouple 4A and a second thermocouple 4B formed on an insulating substrate 1. The first thermocouple 4A is formed by connecting a metal thin-film conductor 3A to a silicon germanium mixed-crystal thin film 2A. The second thermocouple 4B is formed by connecting a metal thin-film conductor 3B to a silicon germanium mixed-crystal thin film 2B.
In this structure, the silicon germanium mixed-crystal thin film of the first thermocouple 4A and the metal thin-film conductor 3B of the second thermocouple 4B are formed parallel to oppose each other.
End portions of the silicon germanium mixed-crystal thin film 2A of the first thermocouple 4A and the metal thin-film conductor 3B of the second thermocouple 4B are connected by a first electrode 5.
A second electrode 6 is connected to the metal thin-film conductor 3A of the first thermocouple 4A.
A third electrode 7 is connected to the silicon germanium mixed-crystal thin film 2B of the second thermocouple 4B.
The electromotive forces of the first and second thermocouples 4A and 4B are added and output to between the second and third electrodes 6 and 7.
Beam lead electrodes 8, 9, and 10 for decreasing the thermal resistance in a cold junction between the first and second thermocouples 4A and 4B are connected to the first, second, and third electrodes 5, 6, and 7, respectively.
This power detector is mounted on a dielectric substrate 11 of a power detecting device shown in FIG. 21.
This dielectric substrate 11 has a transmission line composed of a central conductor 12 having a predetermined width and external conductors 13A and 13B formed parallel with a predetermined spacing between them on the two sides of the central conductor 12.
The beam lead electrode 8 of this power detector 14 constructed as shown in FIG. 20 is connected to the central conductor 12 on the dielectric substrate 11.
The beam lead electrode 9 of the power detector 14 is connected to ground (GND) which communicates with the external conductor 13B on the dielectric substrate 11.
The beam lead electrode 10 of the power detector 14 is connected to an output conductor 15 on the dielectric substrate 11.
The central conductor 12 on the dielectric substrate 11 is connected to a connecting portion 17 via a coupling capacitor 16.
The output conductor 15 on the dielectric substrate 11 is connected to ground (GND) which communicates with the external conductor 13A via a bypass capacitor 18.
A lead line 19A for central conductor output is connected to the output conductor 15.
A lead line 19B for GND output is connected to the ground (GND) which communicates with the external conductor 13B.
FIG. 22 shows an equivalent circuit of this power detecting device.
That is, a signal S to be measured input from the connecting portion 17 is supplied to the two thermocouples 4A and 4B via the coupling capacitor 16, and these two thermocouples 4A and 4B generate heat.
The electromotive forces generated in the two thermocouples 4A and 4B by the heat generated by these two thermocouples 4A and 4B are added and output from the lead lines 19A and 19B.
In the power detecting device constructed as above, the upper-limit value of a band in which the sensitivity lowers by 1 dB extends to 32 GHz.
In addition to the above system (so-called direct heating type), a so-called indirect heating system is also proposed as the thermocouple system. In this indirect heating system, a resistor for converting a power signal to be measured into heat, i.e., an input resistor, and a thermocouple for detecting a temperature rise resulting from the heat generated by this resistor, are separated from each other.
This indirect heating type thermocouple has a longer response time than that of the direct heating type thermocouple. However, the number of thermocouples can be arbitrarily increased independently of the resistor, and a signal having magnitude directly proportional to the number of these thermocouples can be output.
Accordingly, this indirect heating type thermocouple has the advantage that high detectivity is obtained. Thermocouples having frequency characteristics of about 20-odd GHz have been realized.
In the power detector and the power detecting device using the direct heating type thermocouples described above, a signal is supplied to the thermocouples themselves to cause these thermocouples to output DC electromotive forces. Hence, the power of a DC signal cannot be detected. Also, since the capacitance of a capacitor formable on a substrate is limited, the power of a low-frequency signal cannot be accurately detected.
Additionally, in the power detector and the power detecting device using the direct heating type thermocouples described above, the two thermocouples split the load on an input signal, and impedance matching is difficult owing to the influence of the capacitor. Therefore, it is difficult to further extend the upper-limit detection frequency.
Furthermore, in the power detector and the power detecting device using the direct heating type thermocouples described above, a larger number of thermocouples must be provided in the power detecting element in order to detect micro watt power at high sensitivity.
Unfortunately, in the power detector and the power detecting device using the direct heating type thermocouples described above, if the number of thermocouples is increased, the number of necessary capacitors increases accordingly. This makes impedance matching more difficult. As a consequence, the frequency characteristic must be sacrificed.
Especially in recent years, RF communication apparatuses using millimeter waves and microwaves are extensively developed.
To measure these communication apparatuses, it is increasingly demanded to accurately detect the power of signals with higher frequencies. However, the conventional power detecting elements and power detecting devices described above cannot satisfactorily meet this demand.
Also, in the power detector and the power detecting device using the direct heating type thermocouples described above, electronic materials forming the input resistor and the thermocouple are different. This complicates the manufacturing method. Additionally, no knowledge for effectively controlling the difference between the shape of the input resistor electrode and the shape of the resistor has been obtained.
That is, in the power detector and the power detecting device using the direct heating type thermocouples, no knowledge about optimum wiring patterns for connecting the input resistor electrode to the resistor has been obtained. Consequently, the upper limit of measurable frequencies is about 20-odd GHz as mentioned earlier.
The present invention has been made in consideration of the above situation, and has as its object to provide a wide-band RF signal power detecting element which is easy to manufacture, has a high upper-limit detection frequency, can detect power from direct current, and has a frequency characteristic not influenced by the number of thermocouples.
It is another object of the present invention to provide a power detecting device using a wide-band RF power detecting element which is easy to manufacture, has a high upper-limit detection frequency, can detect power from direct current, and has a frequency characteristic not influenced by the number of thermocouples.
According to one aspect of the present invention, there is provided a wide-band RF signal power detecting element comprising
an insulating substrate,
a thin-film resistor formed on the substrate to absorb power of a signal to be measured and generate heat,
first and second ground electrodes formed by thin-film conductors, adjacent to an edge of the substrate, and separated from each other,
a first thin-film connecting portion formed on the substrate to electrically connect the first ground electrode to the thin-film resistor,
a second thin-film connecting portion formed on the substrate to electrically connect the second ground electrode to the thin-film resistor, made to narrow a gap between the first and second thin-film connecting portions toward the thin-film resistor, and connected to the thin-film resistor with the thin-film resistor interposed between the first and second thin-film connecting portions, and
a thin-film thermocouple formed adjacent to and away from the thin-film resistor with a predetermined gap between them to detect a temperature rise of the thin-film resistor.
According to another aspect of the present invention, there is provided a wide-band RF signal power detecting element comprising
an insulating substrate,
at least one thin-film resistor formed on the substrate to absorb power of a signal to be measured and generate heat,
first and second ground electrodes formed by thin-film conductors, adjacent to an edge of the substrate, and separated from each other,
a first thin-film connecting portion formed on the substrate to electrically connect the first ground electrode to the at least one thin-film resistor,
a second thin-film connecting portion formed on the substrate to electrically connect the second ground electrode to the at least one thin-film resistor, and made to narrow a gap between the first and second thin-film connecting portions toward the at least one thin-film resistor,
an input electrode formed adjacent to the edge of the substrate and between the first and second ground electrodes,
an input connecting portion connected to the at least one thin-film resistor, with the at least one thin-film resistor interposed between the first and second thin-film connecting portions, to electrically connect the input electrode to the at least one thin-film resistor, such that a width of the input connecting portion decreases from the input electrode toward the at least one thin-film resistor, and that gaps between the input connecting portion and the first and second thin-film connecting portions narrow toward the at least one thin-film resistor, and
a thin-film thermocouple formed adjacent to and away from the at least one thin-film resistor with a predetermined gap between them to detect a temperature rise of the at least one thin-film resistor.
According to still another aspect of the present invention, there is provided a power detecting device comprising
a power detecting element comprising
an insulating substrate,
at least one thin-film resistor formed on the substrate to absorb power of a signal to be measured and generate heat,
first and second ground electrodes formed by thin-film conductors, adjacent to an edge of the substrate, and separated from each other,
a first thin-film connecting portion formed on the substrate to electrically connect the first ground electrode to the at least one thin-film resistor,
a second thin-film connecting portion formed on the substrate to electrically connect the second ground electrode to the at least one thin-film resistor, and made to narrow a gap between the first and second thin-film connecting portions toward the at least one thin-film resistor,
an input electrode formed adjacent to the edge of the substrate and between the first and second ground electrodes,
an input connecting portion connected to the at least one thin-film resistor, with the at least one thin-film resistor interposed between the first and second thin-film connecting portions, to electrically connect the input electrode to the at least one thin-film resistor, such that a width of the input connecting portion decreases from the input electrode toward the at least one thin-film resistor, and that gaps between the input connecting portion and the first and second thin-film connecting portions narrow toward the at least one thin-film resistor, and
a thin-film thermocouple formed away from the at least one thin-film resistor with a predetermined gap between them to detect a temperature rise of the at least one thin-film resistor, and
a module substrate made larger than the substrate of the wide-band RF signal power detecting element, and comprising a central conductor and a ground conductor formed by patterning on one surface of the module substrate to guide a signal to be measured, and mount portions formed, in one-to-one correspondence with the electrodes of the wide-band RF signal power detecting element, at a distal end of the central conductor and in a portion of the ground conductor in the vicinity of the distal end of the central conductor, the module substrate fixing the wide-band RF signal power detecting element to the one surface with the electrodes of the power detecting element joined to the mount portions, supplying a signal to be measured to between the electrodes of the wide-band RF signal power detecting element, and outputting a signal corresponding to power of the signal to be measured,
characterized in that transmission impedance between the central conductor and the ground conductor of the module substrate is made substantially equal to transmission impedance between the electrodes of the wide-band RF signal power detecting element, and the central conductor is given an inductance component corresponding to a capacitance component increased by junctions between the mount portions and the electrodes of the wide-band RF signal power detecting element.